The present invention pertains to osteoprotegerin obtainable from milk sources, and in particular, from human or bovine milk. The present invention also relates to the use of osteoprotegerin for preparing an ingestible preparation and/or a pharmaceutical composition, in particular for use in a method for preventing or treating disorders associated with bone metabolism or immune function.
In mammals, the bones provide support for the body and consist of minerals, a matrix of collagenous and non-collagenous proteins, and a cellular component. The growth and maintenance of such components are controlled by a variety of different factors involving regulation and interaction of its component cell types, i.e., the chondrocytes which form cartilage, the osteoblasts which synthesize and deposit bone matrix, and the osteoclasts responsible for resorption of bone material.
Chondrocytes are derived from mesenchymal cells and generate an initial cartilage template required for endochondral bone formation. Osteoblasts, which promote formation of bone tissue, are derived from mesenchymal osteoprogenitor cells and are located on the surface of bones where they synthesize, transport and arrange the matrix proteins. On the other hand, osteoclasts, which are responsible for bone resorption, are derived from granulocyte-monocyte precursors present in the hematopoietic marrow. The actions of osteoclasts and osteoblasts are tightly linked e.g., during the process of osteoclast mediated resorption, the protein factors which are elaborated act as signaling molecules to initiate bone renewal by osteoblasts. Osteoblasts, in turn, may influence osteoclast function through expression of soluble or membrane bound regulators. Normal bone remodeling is therefore dependent on a definite balance between the opposing functions of bone formation and bone resorption as conveyed by each of the respective cell types.
Growth factors such as fibroblast growth factor (FGF) and transforming growth factor (TGF)-β are stored in the bone extracellular matrix and when secreted stimulate the local release of bone progenitor cells. Thereafter, factors such as bone morphogenetic proteins (BMPs) and parathyroid hormone (PTH) influence the development to these progenitors into osteoblasts, the bone-forming cells, whose final differentiation and function are regulated by the interaction of the cell with bone matrix proteins.
During ageing an individual is subject to a gradual loss in bone mass, a phenomenon termed uncoupling, which is deemed to result from the activity of osteoclasts exceeding that of osteoblasts. In cases where this uncoupling persists for a longer period of time, more and more of the bone's material gets destroyed/resorbed and a condition called osteoporosis results.
Apart from the age-dependent phenomenon, bone loss may also be brought about by calcium or hormonal deficiency or by conditions which result in a variety of different diseases such as osteoporosis, hypercalcemia, Paget's disease of bone, bone loss due to osteoarthritis or rheumatoid arthritis or osteomyelitis, and the like. The reduced bone density generally leads to a decreased mechanical strength and increased likelihood of fracture.
Current approaches for the treatment of osteoporosis and/or related bone disorders include the use of calcium administered to the individual in need thereof. Recently, agents involved in the stimulation and/or inhibition of bone cells, such as hormones, calcitonin, insulin-like growth factor or osteoprotegerin (OPG) have also been envisaged to be usable in treating the above disease conditions. These agents are generally prepared by recombinant means and have to be formulated/prepared in a galenic form such that the respective substance may reach the target, the bone, in an active form.
PCT publication WO 00/24771 discloses nucleic acids encoding osteoprotegerin like proteins and their use in e.g. the treatment of osteoporosis. The polypeptide is synthesized by recombinant means and then formulated to be compatible with the intended route of administration. Intravenous, intradermal, subcutaneous, oral (e.g. inhalation), transdermal (topical), transmucosal and rectal administrations can be used.
In general, it is quite time-consuming and cumbersome to find a suitable galenic form for a given substance, since the ingredients utilized for this purpose must be compatible with the active substance and must also provide sufficient protection against the different conditions in the body. However, since agents stimulating bone growth are synthesized locally—in or at the bone tissue—it is difficult to administer such a substance. Normally, capsules have to be devised which assist in passing the substance through the gastro-intestinal tract without getting destroyed by the adverse environmental conditions prevailing therein. However, this route of administration also has some drawbacks since the substance has to pass the liver and be transported in body fluids before it reaches the bone. Furthermore, it often leads to a reduced amount of active biological material reaching the target tissue.
Consequently, this presents a problem as to how to provide a means of administering an active substance to an individual, whereby the substance acts in a specific target tissue in the individual. This problem now has been solved by the present invention.